1. Field of the Invention
This invention relates to a drawing data producing apparatus and a drawing data producing method for carrying out so called Z-sorting (sorting in Z (depth) direction) by using one or more sequence tables to produce drawing (painting) data, and is applied to, e.g., a three-dimensional picture display in computer graphics.
2. Description of the Related Art
In a three-dimensional picture display in computer graphics, since it is necessary to produce (prepare) drawing (painting) data so as not to display the portion invisible from the observer's eye, e.g., an original picture is divided into a plurality of blocks to prepare pointers indicating processing sequences for every block from information in the Z (depth) direction in three-dimensional coordinates of respective blocks to write them into a buffer memory, and to register their headers into a table to carry out processing in a block unit in accordance with a sequence designated by the header and the pointer.
An original picture is divided into (64.times.96) blocks as, e.g., unit block of (8.times.8) pixels. Coordinate positions are determined in the in Z-direction in three dimensional coordinates every representative pixels of respective blocks to allow the depth to be in the range of O.about.D to register, as header (start address), block No. (n, m) of the first block having representative pixel of depth d into a table having depth z as address. A series of block numbers starting from the header (start address) are written into a memory as pointer to prepare sequence tables prescribing processing sequences from shallow portion toward deep portion in block units to produce drawing data by Z-sorting using these sequence tables.
Namely, in the case where depth of the representative pixel of a block of block No. (n, m) is d, if any address data is not written in d address of a table, the block number (n, m) is written into the d address of the table as start address. On the other hand, when start address (n.sub.0, m.sub.0) is already written in the d address as shown in FIG. 10, pointer value (n.sub.1, m.sub.1) of (n.sub.0, m.sub.0) address of memory is written into (n, m) address of the memory, and pointer value (n, m) is written into (n.sub.0, m.sub.0) address. By repeating such procedure, a series of block numbers starting from the header (start address) of the table are written into memory as a pointer, thus to prepare sequence tables prescribing processing sequences from shallow portion toward deep portion in block units. Then, drawing data is produced (prepared) by Z-sorting using these sequence tables.
Meanwhile, in conventional drawing data producing apparatus adapted for producing drawing data by Z-sorting using sequence table, in the case where two objects physically divided exist at depths z close to each other, it was disadvantageously unable to exclude interference of polygon unit. In addition, sequence tables corresponding to the range of stages of depth are required. Improvement in accuracy of sequence table resulted in the problem that a memory of a large capacity is required.